You can delete a small part of the mesh to make a hole. Then Copy, Scale down, and Reverse to make the inner surface. And finally there is a command "Stitch Holes" that will join the two surfaces with new triangles.

Of course this depends on the original mesh being a single continuous surface, and being able to shift the inner surface carefully to get the required width without accidental self intersections.

Next week, I'm more than likely purchasing a Rostock Delta 3d Printer. I've been messing around in Blender and Sculptris for 3d printing. I was able to review a Lulzbot TAZ for about a week. Made a visor replacement for my Honda Element in Blender. It took about 3 to 3.5 hours to print. I printed it in halves and chemically bonded them together with acetone. Here are some pictures of the visor clip, the original clip, and then the new part working in my car.

C is missing : Scream's pain of Clicking dost my Keyboard a Thinkin'. I need a new Laptop.

Blender now has native 3d Printing support, which I use. I have a mini factory in my living room right now. 2 printers. I've gotten to use lots of brilliant filaments. Some good, some excellent, and some... just garbage. Nonetheless, it's been super fun 3d printing!

Very cool! I hear the space station has a really fancy one of these 3D printers in case they have to make a tool or something. Even the researchers are using some that make parts for humans using cells etc. etc. etc.

I’m looking forward to try that in my Startrek models. And yes, I'm a bit excited to print something from Curvy with 3d2print's filaments. I have in mind a couple of things to print already like a mini helicopter and battleship for my son.